Ink jet printhead that incorporates through-chip ink flow control

ABSTRACT

An ink jet printhead chip that is the product of an integrated circuit fabrication technique includes a wafer substrate having a front surface and a rear surface. A plurality of ink passages are defined through the wafer substrate, so that each ink passage defines an inlet at a rear surface of the wafer substrate and an outlet at a front surface of the wafer substrate. Each ink passage is in fluid communication with an ink supply at the rear surface of the wafer substrate. A plurality of closure members is positioned on the rear surface of the substrate and each closure member is displaceable between open and closed positions to control a flow of ink through each passage.

REFERENCES TO U.S. APPLICATIONS

[0001] This application is a continuation application of U.S. patentapplication Ser. No. 09/900,159. U.S. Pat. Nos. 6,227,652, 6,213,589,6,247,795, 6,394,581, 6,244,691, 6,257,704, 6,416,168, 6,220,694,6,234,610, 6,247,793, 6,264,306, 6,241,342, 6,254,220, 6,302,528,6,239,821, and 6,247,796 are hereby incorporated by reference. U.S.patent application Ser. No.'s 09/113,121 and 09/113,122 are also herebyincorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates to ink jet printheads. More particularly,this invention relates to an ink jet printhead that incorporatesthrough-chip ink flow control.

BACKGROUND TO THE INVENTION

[0003] The Applicant has invented an ink jet printhead that is capableof generating text and images at a resolution of up to 1600 dpi.

[0004] In order to achieve this, the Applicant has made extensive use ofmicro electro-mechanical systems technology. In particular, theApplicant has developed integrated circuit fabrication techniquessuitable for the manufacture of such printheads. The Applicant has fileda large number of patent applications in this field, many of which havenow been allowed.

[0005] The printheads developed by the Applicant can include up to 84000nozzle arrangements. Each nozzle arrangement has at least one movingcomponent that serves to eject ink from a nozzle chamber. The componentsusually either act directly on the ink or act on a closure which servesto permit or inhibit the ejection of ink from the nozzle chamber.

[0006] The moving components within the printheads are microscopicallydimensioned. This is necessary, given the large number of nozzlearrangements per printhead. The Applicant has spent a substantial amountof time and effort developing configurations for such printheads.

[0007] One of the reasons for this is that, as is known in the field ofintegrated circuit fabrication, cost of on-chip real estate is extremelyhigh. Furthermore, it is important that levels of complexity are kept toa minimum since these significantly increase the cost of fabrication.

[0008] Integrated circuit fabrication techniques involve what isgenerally a deposition and etching process. As a result, devices thatare manufactured in accordance with such techniques are usually, ofnecessity, in a layered construction. Furthermore, it is important todevelop a configuration where a high number of devices can be fabricatedper unit area of chip surface.

[0009] The present invention has been conceived by the Applicant toaddress the difficulties associated with achieving the high packingdensity of the nozzle arrangements and thereby to facilitate substantialcost saving in manufacture.

SUMMARY OF THE INVENTION

[0010] According to a first aspect of the invention, there is providedan ink jet printhead chip that is the product of an integrated circuitfabrication technique, the printhead chip comprising

[0011] a wafer substrate having a front surface and a rear surface, aplurality of ink passages being defined through the wafer substrate, sothat each ink passage defines an inlet at a rear surface of the wafersubstrate and an outlet at a front surface of the wafer substrate, eachink passage being in fluid communication with an ink supply at the rearsurface of the wafer substrate; and

[0012] a plurality of actuators that are positioned on the rear surfaceof the wafer substrate and are operatively arranged with respect to theink passages to generate an ink flow through each passage, from the rearsurface to the front surface, when activated.

[0013] According to a second aspect of the invention, there is providedan ink jet printhead chip that is the product of an integrated circuitfabrication technique, the ink jet printhead chip comprising

[0014] a wafer substrate;

[0015] a plurality of ink passages defined through the wafer substrate,so that each ink passage defines an inlet at a rear surface of the wafersubstrate and an outlet at a front surface of the wafer substrate, eachink passage being in fluid communication with an ink supply at the rearsurface of the wafer substrate;

[0016] roof walls, side walls and floor walls that are positioned on therear surface of the wafer substrate to define a plurality of nozzlechambers, each roof wall defining an ink ejection port that is in fluidcommunication with a respective ink passage; and

[0017] a plurality of actuators that are positioned on the rear surfaceof the wafer substrate so that each actuator is operatively arrangedwith respect to each nozzle chamber to eject ink from the nozzle chamberand out of the ink ejection port.

[0018] The invention is now described, by way of examples, withreference to the accompanying drawings. The specific nature of thefollowing description is not to be construed as limiting the scope ofthe above summary, in any way.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the drawings,

[0020]FIG. 1 shows a three dimensional view of a first embodiment ofpart of a printhead chip, in accordance with the invention;

[0021]FIG. 2 shows a sectioned side view of the printhead chip of FIG.1;

[0022]FIG. 3 shows a sectioned side view of a second embodiment of aprinthead chip, in accordance with the invention, with a nozzlearrangement of the printhead chip in a pre-operative condition;

[0023]FIG. 4 shows the nozzle arrangement of FIG. 3, in a post-operativecondition;

[0024]FIG. 5 shows a side sectioned view of a third embodiment of aprinthead chip, in accordance with the invention, with a nozzlearrangement of the printhead in a pre-operative condition;

[0025]FIG. 6 shows a side sectioned view of the nozzle arrangement ofFIG. 5, in a post-operative condition; and

[0026]FIG. 7 shows a sectioned side view of a fourth embodiment of aprinthead chip, in accordance with the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] In the drawings, reference is made to a nozzle arrangement. Itwill be appreciated that the printhead chip of the invention comprises aplurality of the nozzle arrangements. Furthermore, as set out in thepreamble, the printhead chips can incorporate an extremely high numberof such nozzle arrangements. Accordingly, only one nozzle arrangement isshown in each of the drawings, for the sake of convenience and for easeof description. It will readily be appreciated that replicating each ofthe nozzle arrangements to a sufficiently high degree will provide areader with a configuration of the printhead chip, in accordance withthe invention.

[0028] In FIGS. 1 and 2, reference numeral 10 generally indicates anozzle arrangement of a printhead chip, in accordance with theinvention.

[0029] The nozzle arrangement 10 includes a substrate 12 forming part ofthe printhead chip of the invention. The substrate 12 includes a wafersubstrate 14. An epitaxial layer 16 of boron doped silicon is depositedon a front surface of the wafer substrate 14. The epitaxial layer 16thus defines an etch stop layer 18. The wafer substrate 14 is etched todefine a nozzle chamber 20 so that the etch stop layer 18 defines a roofwall 22 of the nozzle chamber 20.

[0030] The roof wall 22 is itself etched to define an ink ejection port23. It follows that the nozzle chamber 20 and the ink ejection port 23together define an ink passage through the wafer substrate 14.

[0031] A drive circuitry layer 24 is positioned on a rear surface of thewafer substrate 14 and incorporates drive circuitry (not shown) for thenozzle arrangement 10. An ink passivation layer 26 of silicon nitride isdeposited on the drive circuitry layer 24.

[0032] In this particular embodiment, a shutter member or shutter 28 ispositioned on the layer 26 and is displaceable between a closed positionin which the shutter 28 covers an inlet 30 of the nozzle chamber 20 andan open position in which ink is permitted to flow into the nozzlechamber 20. The shutter 28 has a toothed edge 32.

[0033] The nozzle arrangement 10 includes a micro electro-mechanicaldrive mechanism 34 to drive the shutter 28 between its closed and openpositions. In particular, the drive mechanism 34 includes a series ofgears 36, 38, 40 that engage the toothed edge 32 of the shutter 28. Inparticular, actuators 42 drive the gear 36. The gear 36 is engaged withthe gear 38, which, in turn, is engaged with the gear 40. The gears 36,38, 40 are configured to achieve a reduction effect on the gear 40. Thegear 40 is engaged with the toothed edge 32.

[0034] The actuators 42 are electrically connected to the drivecircuitry layer 24 to be controlled via a suitable control system (notshown), which, in turn, is connected to the drive circuitry layer 24.

[0035] The drive mechanism 34, the ink passivation layer 26 and theshutter 28 are all in fluid contact with an ink reservoir 44 (shown inFIGS. 3 to 6).

[0036] In this embodiment, the ink within the ink reservoir 44 isrepeatedly pressurized to an extent sufficient to facilitate theejection of ink from the ink ejection port 23. Thus, by controllingoperation of the shutter 28 via the drive circuitry layer 24 and thedrive mechanism 34, selective ejection of ink from the ink ejection port23 can be achieved.

[0037] It will be appreciated that, in this embodiment, the ink isejected through the wafer substrate 14 from the rear surface of thewafer substrate 14 towards the front surface of the wafer substrate 14.

[0038] Details of the operation of the drive mechanism 34 and of theremainder of the nozzle arrangement 10 are set out in the abovereferenced U.S. applications. It follows that this detail will not becovered in this specification.

[0039] In FIGS. 3 and 4, reference numeral 50 generally indicates anozzle arrangement of a second embodiment of a printhead chip, inaccordance with the invention. With reference to FIGS. 1 and 2, likereference numerals refer to like parts, unless otherwise specified.

[0040] Instead of the shutter 28 used in combination with the repeatedlypressurized ink to achieve drop ejection, the nozzle arrangement 50includes an actuator 52 which acts directly on ink 54 in the nozzlechamber 20.

[0041] The actuator 52 includes a heater element 56 that is of a shapememory alloy. In this particular example, the shape memory alloy is anickel titanium alloy.

[0042] Details of the shape memory alloy are provided in the abovereferenced U.S. applications and are therefore not set out in thisspecification.

[0043] The heater element 56 has a trained shape as shown in FIG. 4. Alayer 58 of silicon nitride is deposited, under tension, on the heaterelement 56, with the heater element 56 in its martensitic phase. Thiscauses the heater element 56, together with the layer 58, to bend awayfrom the ink ejection port 23, as shown in FIG. 3.

[0044] The heater element 56 is connected to the drive circuitry layer24 with suitable vias 60. Furthermore, the heater element 56 isconfigured to be resistively or joule heated when a current from thedrive circuitry layer 24 passes through the heater element 56. This heatis sufficient to raise the temperature of the heater element 56 aboveits transformation temperature. This results in the heater element 56undergoing a crystalline change into its austenitic phase, therebyreverting to its trained shape as shown in FIG. 4. The resultantmovement results in the generation of a drop 62 of ink.

[0045] When the heater element 56 cools, the tension that has built upin the layer 58 results in the heater element 56, now in its martensiticphase, returning to the position shown in FIG. 3. This facilitatesnecking and separation of the drop 62.

[0046] In FIGS. 5 and 6, reference numeral 70 generally indicates anozzle arrangement of a third embodiment of a printhead chip, inaccordance with the invention. With reference to FIGS. 1 to 4, likereference numerals refer to like parts, unless otherwise specified.

[0047] The nozzle arrangement 70 includes an actuator 72 that also actsdirectly on the ink 54 within the nozzle chamber 20. However, in thiscase, the actuator 72 is hingedly connected to the substrate 12 to behingedly displaceable between the pre-operative position shown in FIG. 5and the post-operative position shown in FIG. 6.

[0048] The actuator 72 has a magnetic core 74 that is susceptible to amagnetic field of cyclically reversing polarity applied to the printheadchip. The cyclically reversing magnetic field tends to cause theactuator 72 to oscillate between the positions shown in FIGS. 5 and 6.The magnetic core 74 is sufficiently sensitive and the magnetic fieldsufficiently strong so that this oscillation, if unchecked, results inthe ejection of the drop 62 of the ink 54 from the ink ejection port 23.

[0049] The nozzle arrangement 70 includes a checking or obstructionmechanism 78 that is positioned in a side wall 80 of the nozzle chamber20. The obstruction mechanism 78 is connected to the drive circuitrylayer 24 to be controlled with a suitable control system (not shown)also connected to the drive circuitry. The obstruction mechanism 78 isconfigured so that, when activated, an obstruction member 82 of themechanism 78 extends from the side wall 80 into the nozzle chamber 20.As can be seen in FIG. 5, this serves to obstruct movement of theactuator 72 into the nozzle chamber 20.

[0050] It will thus be appreciated that selective ejection of the ink 54from the ink ejection port 23 can be achieved.

[0051] As with the previous embodiments, detail of the working andstructure of the nozzle arrangement 70 is set out in the abovereferenced U.S. applications. The primary purpose of illustrating theseexamples is to indicate possible configurations that can be achievedwhen the ink is displaced from the rear surface of the wafer substrate14 to the front surface, through the wafer substrate 14.

[0052] In FIG. 7, reference numeral 90 generally indicates a nozzlearrangement of a fourth embodiment of a printhead chip, in accordancewith the invention. With reference to FIGS. 1 to 6, like referencenumerals refer to like parts, unless otherwise specified.

[0053] In the nozzle arrangement 90, the wafer substrate 14 is etched todefine an ink ejection channel 92. Furthermore, the nozzle chamber 20 isdefined by an ink ejection paddle 94 positioned behind the inkpassivation layer 26, side walls 96 extending from the ink passivationlayer 26 and a roof wall 98 spanning an inlet 100 to the ink ejectionchannel 92. Thus, the ink ejection paddle 94 defines a floor wall of thenozzle chamber 20. The roof wall 98 defines an ink ejection port 102. Itfollows that the ink ejection port 102 and the ink ejection channel 92together define an ink passage through the wafer substrate 14.

[0054] The ink ejection paddle 94 is shaped to define an included volume104 that forms part of the nozzle chamber 20. Furthermore, the inkejection paddle 94 is partially received within the side walls 96. Thus,on displacement of the ink ejection paddle 94 towards the roof wall 98,a volume of the nozzle chamber 20 is reduced so that ink is ejected fromthe ink ejection port 102 to pass through the ink ejection channel 92and on to the print medium. An arrow 106 indicates the direction ofmovement of the ink ejection paddle 94.

[0055] The ink ejection paddle 94 is connected to a thermal actuatingdevice 108. In order to protect the device 108, a silicon nitrideenclosure 110 is positioned on the passivation layer 26 to enclose thedevice 108.

[0056] The device 108 includes a deformable body 116 of expansionmaterial having a coefficient of thermal expansion, which is such that,upon heating, expansion of the material can be harnessed to performwork. The body has a proximal planar surface 120, closest to the wafersubstrate 14, and an opposed distal planar surface 122. The device 108includes a heater element 118 that is positioned in the body 116 to heatthe body 116. As can be seen in FIG. 7, the heater element 118 ispositioned closest to the distal surface 122. Thus, when the heaterelement 118 is activated, the expansion material in a region proximatethe distal surface 122 expands to a greater extent than the remainingmaterial. This results in the body 116 bending towards the substrate 14.

[0057] The body 116 is elongate, with one end attached to a support post124 to provide a bending anchor. An opposed end of the body 116 is freeto move. The heater element is connected to the drive circuitry layer 24with a suitable via 126 in the support post 124.

[0058] An arm 112 interconnects the body 116 with the ink ejectionpaddle 94. In order to achieve this, the arm 112 extends through afluidic seal 114 that is positioned in a wall 128 of the silicon nitrideenclosure 110.

[0059] The enclosure 110, the ink ejection paddle 94 and the side walls96 are all positioned in an ink reservoir, indicated at 130. The paddle94 and the side walls 96 are positioned so that ink is permitted to flowinto the nozzle chamber 20 from the ink reservoir 130, subsequent todisplacement of the paddle 94 away from the ink ejection port 102.

[0060] A particular advantage of this configuration is that the ink isejected from a point at the rear surface of the wafer substrate 14 topass through the wafer substrate 14. As a result, special preparation ofthe front surface of the wafer substrate is not necessary. Thissimplifies the fabrication of the printhead chip with a resultant costsaving.

We claim
 1. An ink jet printhead chip that comprises a substrate having a front surface and a rear surface, a plurality of ink passages being defined through the substrate, so that each ink passage defines an inlet at the rear surface of the wafer substrate and an outlet at the front surface of the wafer substrate, each ink passage being in fluid communication with an ink supply at the rear surface of the wafer substrate; and a plurality of closure members corresponding to respective passages, the closure members being positioned on the rear surface of the substrate and each closure member being displaceable between open and closed positions to control a flow of ink through each passage.
 2. An ink jet printhead chip as claimed in claim 1, in which a plurality of actuators are positioned on the rear surface of the wafer substrate and are operatively engaged with the closure members to displace the closure members between the open and closed positions, when activated.
 3. An ink jet printhead chip as claimed in claim 2, in which a drive circuitry layer is positioned on the rear surface of the wafer substrate and is electrically connected to the actuators, so that the actuators can be activated by a signal received from the drive circuitry layer.
 4. An ink jet printhead chip as claimed in claim 1, in which said each ink passage defines a nozzle chamber in the wafer substrate.
 5. An ink jet printhead chip as claimed in claim 4, in which an etch stop layer is positioned on the front surface of the wafer substrate to provide an etch stop for etching of the wafer substrate to define the nozzle chambers so that the etch stop layer defines a roof wall of each nozzle chamber, an ink ejection port being defined in each roof wall as a result of an etching process carried out on the roof wall so that the ink ejection port defines the outlet of the ink passage.
 6. An ink jet printhead chip as claimed in claim 2, in which each closure member defines an ink displacement member that is operatively positioned with respect to the inlet of its respective ink passage and is displaceable between pre-operative and post-operative positions to direct ink from the inlet of the ink passage to the outlet, so that ink is ejected from the outlet, and each actuator includes an actuating mechanism to move the ink displacement member between the pre-operative and post-operative positions.
 7. An ink jet printhead chip as claimed in claim 1, in which the wafer substrate defines a plurality of ink channels forming part of respective ink passages. 